can not与 cannot的区别

连续两篇文章中都被圈出这个错误，感谢强大的google搜索引擎，终于学习如下：

Can的否定形式是什么？Can’t。没错。如果不缩写是什么？Can not。错了。应该是cannot，一个词，而不是分开两个词。

这个错误我以前也犯过不计其数次。当然，我有借口——国内的课本里没教过。（至少我读初中的时候，老师绝对没有讲过这一点。）两年前我读newspaper reporting的课程时，每次稿子里的can not都被老师用红笔圈出来，我才意识到这是个错误。

为什么不可以搞混？简单地说，因为两者的意思完全不同。Cannot是“不可以”，而can not是“可以不”。举个例子：

I cannot believe this! （我无法相信！等于I can’t believe this!）
I can not believe this! （我可以不相信！也就是说：I can believe this, or I can not believe this. 我并不一定要相信，我可以选择不相信。）

在网上找到一篇非常不错的帖子，摘录如下：

What we should use when we mean “are unable to” or “are not permitted to” is one word: cannot. This is the word that we contract when we write “can’t.” It is a common error to separate “can” and “not.” The American Heritage Dictionary is quite clear on this point: cannot is the negative form of the word can.

Here’s one example I use:
If I say “I cannot smoke,” I mean that I am unable to or not permitted to smoke. If I say, “I can not smoke,” not modifies smoke. My meaning is: “I am able to not smoke,” i.e., I have the ability to avoid smoking, to prevent myself from smoking, or to stop smoking.

Another example:
If I am unable to go or am not permitted to go, I should write, “I cannot go.” If I have a choice between going and not going, I may write, “I can go, or I can not go – it is my choice.”

To all my fellow nitpickers out there: I am fully aware that the two-word construction “can not” is often used where the opposite of “can” is intended. Despite the ubiquity of this usage, it is still an error.